From 7c88260900ccff2bc8eb06365c0ba26507a9fd36 Mon Sep 17 00:00:00 2001
From: Christos Choutouridis <hoo2@hoo2.net>
Date: Mon, 11 Nov 2024 21:16:54 +0200
Subject: [PATCH] WIP: A fisrst V0 approach - no .mat file support

---
 homework_1/Makefile                     |   4 +-
 homework_1/report/homework_1_report.tex |   2 +-
 homework_1/src/main.cpp                 | 108 ++++++++++++++++++++++--
 3 files changed, 103 insertions(+), 11 deletions(-)

diff --git a/homework_1/Makefile b/homework_1/Makefile
index ac341b5..3c5593b 100644
--- a/homework_1/Makefile
+++ b/homework_1/Makefile
@@ -76,7 +76,7 @@ CSIZE           := size
 CFLAGS          := $(DEB_CFLAGS)
 CXXFLAGS		:= $(DEB_CXXFLAGS)
 CXX             := g++
-
+CC              := gcc
 
 #
 # =========== Main body and Patterns ===========
@@ -264,7 +264,7 @@ csal_v1: $(BUILD_DIR)/$(TARGET)
 # examples:
 #
 # make IMAGE=hpcimage EXEC=knnsearch_v1 run
-# make IMAGE=hpcimage EXEC=knnsearch_cilkv1 run
+# make IMAGE=hpcimage EXEC=knnsearch_v1 run
 #
 run: DOCKER := $(DOCKER_CMD)
 run:
diff --git a/homework_1/report/homework_1_report.tex b/homework_1/report/homework_1_report.tex
index dc64304..efbcd41 100644
--- a/homework_1/report/homework_1_report.tex
+++ b/homework_1/report/homework_1_report.tex
@@ -1,5 +1,5 @@
 %
-% Network programming Lab sum report
+% PDS homework_1 report
 %
 % authors:
 %   Χρήστος Χουτουρίδης ΑΕΜ 8997
diff --git a/homework_1/src/main.cpp b/homework_1/src/main.cpp
index 5b2e1d5..425332d 100644
--- a/homework_1/src/main.cpp
+++ b/homework_1/src/main.cpp
@@ -1,15 +1,107 @@
 #include <iostream>
 #include <cblas.h>
+#include <cmath>
+#include <vector>
+#include <algorithm>
+#include <queue>
+
+/*!
+ * Function to compute squared Euclidean distances
+ *
+ * \fn void pdist2(const double*, const double*, double*, int, int, int)
+ * \param X    m x d matrix
+ * \param Y    n x d matrix
+ * \param D2   m x n matrix to store distances
+ * \param m    number of rows in X
+ * \param n    number of rows in Y
+ * \param d    number of columns in both X and Y
+ */
+void pdist2(const double* X, const double* Y, double* D2, int m, int n, int d){
+   // Compute the squared norms of each row in X and Y
+   std::vector<double> X_norms(m), Y_norms(n);
+   for (int i = 0; i < m; ++i) {
+      X_norms[i] = cblas_ddot(d, X + i * d, 1, X + i * d, 1);
+   }
+   for (int j = 0; j < n; ++j) {
+      Y_norms[j] = cblas_ddot(d, Y + j * d, 1, Y + j * d, 1);
+   }
+
+   // Compute -2 * X * Y'
+   cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasTrans, m, n, d, -2.0, X, d, Y, d, 0.0, D2, n);
+
+   // Step 3: Add the squared norms to each entry in D2
+   for (int i = 0; i < m; ++i) {
+      for (int j = 0; j < n; ++j) {
+         D2[i * n + j] += X_norms[i] + Y_norms[j];
+         D2[i * n + j] = std::max(D2[i * n + j], 0.0); // Ensure non-negative
+         D2[i * n + j] = std::sqrt(D2[i * n + j]);     // Take the square root of each
+      }
+   }
+}
+
+void quickselect(std::vector<std::pair<double, int>>& vec, int k) {
+   std::nth_element(
+      vec.begin(),
+      vec.begin() + k,
+      vec.end(),
+      [](const std::pair<double, int>& a, const std::pair<double, int>& b) {
+         return a.first < b.first;
+   });
+   vec.resize(k);  // Keep only the k smallest elements
+}
+
+// K-nearest neighbor search function
+void knnsearch(const double* C, const double* Q, int m, int n, int d, int k,
+               std::vector<std::vector<int>>& idx, std::vector<std::vector<double>>& dst) {
+    std::vector<double> D(m * n);
+    pdist2(C, Q, D.data(), m, n, d);
+
+    idx.resize(n, std::vector<int>(k));
+    dst.resize(n, std::vector<double>(k));
+
+    for (int j = 0; j < n; ++j) {
+        // Create a vector of pairs (distance, index) for the j-th query
+        std::vector<std::pair<double, int>> dst_idx(m);
+        for (int i = 0; i < m; ++i) {
+           dst_idx[i] = {D[i * n + j], i};
+        }
+
+        // Find the k smallest distances using quickSelectKSmallest
+        quickselect(dst_idx, k);
+
+        // Sort the k smallest results by distance for consistency
+        std::sort(dst_idx.begin(), dst_idx.end());
+
+        // Store the indices and distances
+        for (int i = 0; i < k; ++i) {
+            idx[j][i] = dst_idx[i].second;
+            dst[j][i] = dst_idx[i].first;
+        }
+    }
+}
 
 int main(){
 
-   double A[6] = {1.0,2.0,1.0,-3.0,4.0,-1.0};
-   double B[6] = {1.0,2.0,1.0,-3.0,4.0,-1.0};
-   double C[9] = {.5,.5,.5,.5,.5,.5,.5,.5,.5};
-   cblas_dgemm(CblasColMajor, CblasNoTrans, CblasTrans,3,3,2,1,A, 3, B, 3,2,C,3);
+   int m = 5; // Number of points in C (corpus)
+   int n = 3; // Number of points in Q (query)
+   int d = 2; // Dimensions
+   int k = 2; // Number of nearest neighbors to find
+
+   double C[] = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0}; // m x d matrix
+   double Q[] = {1.5, 2.5, 3.5, 4.5, 5.5, 6.5};                     // n x d matrix
+
+   std::vector<std::vector<int>> idx;
+   std::vector<std::vector<double>> dst;
+
+   knnsearch(C, Q, m, n, d, k, idx, dst);
+
+   // Print results
+   for (int i = 0; i < n; ++i) {
+      std::cout << "Query point " << i << ":\n";
+       for (int j = 0; j < k; ++j) {
+          std::cout << "  Neighbor " << j <<": Index = " << idx[i][j] <<", Distance = " << dst[i][j] << '\n';
+       }
+   }
 
-   for (int i=0 ; i<9 ; ++i)
-      std::cout << C[i] << ' ';
-   std::cout << '\n';
-	return 0;
+   return 0;
 }